1. Field of the Invention
The invention relates to the field of rehabilitation. In particular the invention relates to foot and ankle orthoses and methods for using them.
2. Description of the Related Technology
Drop foot is a common medical condition that has its source in various different pathological conditions. The condition can be caused by trauma in which the peroneal nerve that innervates the peroneal muscles is damaged. Drop foot can also be present following a stroke or it can be congenital.
The traditional treatment for drop foot deformity involves the use of a rigid ankle/foot brace also known as an orthosis. The ankle/foot brace maintains the ankle rigid and in a neutral position. This fixed brace, which does not allow motion at the ankle, suffers from several problems. One of the problems is the interference with normal ankle function due to the fact that this brace maintains the ankle rigid. This increases the risk of soft tissue contracture and other pathologies resulting from long-term, joint immobilization. Another problem is that, since the ankle is fixed by the brace and the peroneal muscles are not stimulated, the muscles degenerate and lose their viability and mass. Furthermore, since the ankle joint is held fixed, the ability to perform activities that require ankle movement is limited.
Functional Electrical Stimulation (FES) is a well-established field of research and its foundation is based on the fact that a muscle can be externally stimulated to contract by a current having a specific shape, strength and frequency through skin-electrodes overlying the muscle or through electrodes implanted beneath the skin. Some attempts have been made to use FES in the treatment of patients with drop foot. However, these attempts were quite limited and impractical for everyday use for several reasons. For example, they did not provide a method to consistently apply the electrodes in their optimal location. The stimulation provided was based on very limited and insufficient information from either the leg inclination or from the heel maintaining contact with the ground. No lateral stability was provided and no microprocessor was used to process the input signals and generate appropriate action through stimulation of the peroneal muscles. Finally, and perhaps most importantly, conventional FES is well known to result in quick fatigue of the stimulated muscles. Once fatigue sets in, the muscles can not perform their function appropriately and dropfoot again becomes a problem. Conventional FES methods do not provide means of overcoming or addressing this critical problem.
Therefore there exists a need for providing an FES brace that can be easily applied and maintained by the patient, without the need for intervention of a physical therapist each time the brace must be used and which provides consistent optimal placement of the FES electrodes against the skin each time the brace is applied. This FES brace should also provide controlled, meaningful stimulation of the peroneal muscles based on information from the foot-ground interaction. Finally, the FES brace should provide a means to lock the joint in a fixed position and cease stimulation in a controlled periodic manner thus avoiding the problem of fatigue.